Warnings on multiple access to weakly captured reference in same scope

Development Compiler
1

Is there already some compiler flag that allows this warning, otherwise what would be the best way to pitch this behavior?

When encountering code like:

{ [weak self] in
  self?.prepare()
  self?.doWork()
  self?.cleanup()
}

I'd like the compiler to emit a warning, and offer a fixit that creates a strong reference that persists throughout the scope.

Thanks in advance for any suggestions on how to pursue pitching this or how to access any existing flags.

4 Likes
2

Oof. We have that warning in Clang, but we should certainly have it in Swift as well. For any new warning, though, it's important to have a way to silence it to say "yes, I really do want to recheck self for each of these calls."

5 Likes
3

A definitely terrible way to signal that you want to silence the warning would be to chain multiple calls to self. This is legal:

{ [weak self] in
  self?.self.prepare()
  self?.self.doWork()
  self?.self.cleanup()
}

The fixit could suggest that, and the compiler could use it to infer that you actually meant to have the separate references. But please, please don't solve it like this. I regret posting it, and I haven't even hit the button yet.

1 Like
4

Discourse needs a "laugh" react. :-)

5 Likes
5

Imho that's a job for a linter, not for the compiler.

2 Likes
6

I do this to encapsulate long promise chains that need many weak captures. It works pretty well, but I wouldn't do it for synchronous work, just closures.